Inside coated lamp bulb



Patented June 21, 1932 UNITED STATES PATENT OFFICE AARON MARTIN HAGEMAN, OF BLOOMFIELD, AND ALBERT FERDINAND LINDSTROM,

OF NUTLEY, NEW JERSEY, ASSIGNORS TO WESTINGHOUSE LAMP COMPANY, A COR- PORATION OF PENNSYLVANIA msrnn coa'rnn LAMP BULB No Drawing.

This invention relates to a coated article and to the method of producing the same and more particularly to a glass or vitreous article having an opalescent or colored lustrous appearance and the method of producing such appearance by the use of a coating as set forth in our copending application, Serial No. 7 36,855, filed Sept. 10, 1924, for coating compositions.

While the invention will be described as applied to an incandescent electric lamp bulb, it is to be understood that it is not so limited and may be applied equally well to a large variety of objects, such as-lighting fixtures, globes, shades, etc.

Opalescent effects have heretofore been produced by using opal glass, that is, a glass to which cryolite is added during the manudrofluoric acid or other etching solutions.-

Extreme care must be taken, however, in the handling of such materials and their use is therefore extremely objectionable. Moreover, the effects produced are not lustrous nor of a pearly character.

Heretofore the diificulties' encountered in using opal glass or etched glass were overcome by coating the exterior surface to produce an o alescent efiect.

While this lamp is of excellent appearance and the coating thereon is very durable, it is desirable forcertain purposes that the outer surface of the lamp be smooth and vitreous. This permits the lamp to be more readily cleaned and gives it a lustrous appearance. Moreover, it has been found advisable in coating lamps as set forth in said application, to increase the resistance of the coating Application filed September '18, 1924. Serial No. 737,609.

to atmospheric conditions by baking it on the lamp bulb and treating it with a fixing solution such as ammonium chloride. This operation is somewhat inconvenient and un less care is taken with the use-of the fixing solution, the bases of the lamps become badly corroded thereby.

One of the objects of the present inventionis'to produce a hollow glass or vitreous article having an opalescent on colored lustrous appearance and a smooth vitreous exterior surface. 1

Another object is to produce an incandescent electric lam bulb having an internal superficial light di using coating.

Another object is to produce an inside coated lamp bulb which will have the prop- U erty of diifusing the light with a .minlmum absorption thereof.

Another object is to produce a light diffusing bulb for an incandescent lamp in which the loss of light due to the blackening of the bulb by vaporization from the filament will be greatly reduced.

Another object is to produce an incandescent lamp having a smooth superficial coating of even thickness on the interior surface thereof.

Another object of the invention is to provide a process of producing opalescent highly lustrous effects on hollow Vitreous articles.

Another object is to provide a method of coating an incandescent lamp bulb on the interior surface with a material capable of producing light diffusing opalescent or 001- ored eflects.

Other objects and advantages will hereinsuch as an incandescent lamp. The coating composition may comprise a pigment, a binder, a filler and an lngredlent which serves ,to reduce the melting point of the glass to which a composition is applied and to cause the composition to assume a smooth even coatin on such object. The binder ma be of suc nature that when opalescent e cots are desired, the pigment will be obtained by dehydration thereof although when colored effects are desired, a separate pigment may be added to the composition.

The pigment should be more or less opaque .in order to render the surface to which it is binder should be of the nature suitable for uniting the pigment and filler together and to the object to. which the enamel may be applied. All of the ingredients of the composition must be stable or capable of combining to form compounds which. are stable at the operating temperature of the lamp. Furthermore, it must be-capa-ble .of with standing the heat required to seal the mount into the lamp.

A further requirement is that under the temperature which the lamps attain in operation and the high vacuum which is produced therein, the coating must not give off objectionable gases or vapors which will be deleterious to the filament or lower the efiiciency of the lamp. Furthermore, the composition when applied to the lamp, must assume a smooth even coating of suflicient thickness and opacity to give a pearly white appearance or a lustrous colored effect with a minimum obstruction of light. A still further requirement of the composition or enamel is thatit will not substantially affect the melting point of the glass since otherwise, when the coating is applied to incandescent lamp bulbs, difliculties might be encountered in sealing the mount into the bulb.

It is highly desirable in order to obtain the best results, that the solid ingredients be in a finely divided form since a more intimate mixture is thereby obtained and a smoother and more even coating secured. The filler,

for opalescent effects,.should preferably be white and more or less translucent and the specific gravity of the binder should be relatively high in order that a mixture of the required consistency for securing proper coatings may be obtained with the use of a minimum amount of filler. The coating moreover, should have the property of setting upon the application of heat, into' a compact hard and homogeneous mass containing no volatile constituents.

A composition which has been found to meet all the requirements for a coating of this nature may be. composed of the following ingredients and proportions, although it is to be understood that variations may be made therein without departing from the invention. 200 grams of a filler comprising a very fine grade of pure white kaolin is mixed with 25 grams of an alkali which may be chemically pure sodium hydroxide and 1,000

l c. c. of a binder composed of an aqueous solution of an alkali silicate, preferably sodium silicate having a specific gravity of about 1.2 5.

The kaolin or filler serves to give body to the composition and to give it the right consistency for being properly applied to the.

objects to be coated.

The alkali serves a two-fold function. It

ished or coated article will have a melting point not substantially different from the clear glass.

The sodium silicat acts both as a binder and as apigment for the production of opalescent effects. It is important that the binder has a high specific gravity since the water content thereof, is thereby lowered and there is less moisture present to be removed before the mount is sealed into the bulb. Moreover, by using a binder having a high specific gravity, the amount of filler required to, give the compound the required consistency is thereby reduced and a whiter coating produced,

The pigment, when opaleccnt effects are desired, may be supplied entirely by the sodium silicate and the filler. Then the sodium silicate is dehydrated in a manner which will presently appear, the sodium silicate is left as a fine white opaque material which serves as a pigment for producing the desired effects. Due to the fact that the pigment is formed partially out of the solution, it is very intimately and evenly mixed with the other ingredients of the coating thereby resulting in a uniform distribution over the surface and giving the coating a more uniform whiteness.

When 'iewedthrough the glass, as it must be when coated on the inside of a bulb or other hollow object, a soft lustrous effect similar to that of the pearl is produced.

The appearance is more pleasing than in the case of lamps made from opal glass or when coated on the exterior.

In addition to the pleasing appearance ob- 1 tained by aplying the coating to the inside of the bulb, a more material advantage is obtained in that when such lamps are employed for outdoor use, the coating composition is protected against discoloration or fading under the action of the rays of the sun. It

is common knowledge that coatings, when dishighly resistant to heat and capable of withstanding the temperatures attained in the sealing-in and exhaust operations of manufacturing the lamp.

The mixture is placed in a mixing vessel or ball mill and thoroughly agitated until ahomogeneous mixture is obtained. The coating may be applied to the interior of the lamp bulb or other hollow objects by pouring or spraying or in any other suitable-manner. It is essential, however, that the composition or enamel be of the proper consistency in order that good results may be obtained. However, it the-composition is of the proper consistency, it may be applied to the objects in almost any manner and a. satisfactory coating secured. The composition may be poured into the bulb or sprayed therein and the excess allowed to drain therefrom by gravity. If desired, the bulb or other object may be agitated or its interior subjected to a vacuum to assist in removing the excess enamel although this is not necessary since the excess will drain by gravity from the object in a very few seconds.

The articles or substances which have been coated, are subjected to heat treatment at an elevated temperature of from 200 to 450 C., for three or four minutes to dehydrate the binder and bake the coating thus causing it to become firmly united to the object. The heat also removes all occluded gases which are contained in-the coating and reduces the sodium silicate solution to a fine white crystalline form.

It is essential that all the water vaporbe removed from the coating since the slightest amount of moisture will have a deleterious effect on the filament. However, any gases or water vapor remaining in the coating after the baking operation will be removed during the exhausting of the lamp since the bulb is highly heated at that time.

It is advisable. however, in the case of incandescent electric lamp bulbs, that they be made into completed lamps within a reasonwere coated more than a week prior to being made up into the completed lamp.

It is believed that this inside coating, in addition to producing an opalescent and diffusing efiect, of very high quality, may also have a certain action in preventing blacken-- ing of the bulb. This action may be due to the increased area of the inside of the bulb, caused by the minute irregularities in the coating, whereby the vaporized filament material, assures a thinner film. We do not,

however, care to limit ourselves to any par.- ticular theory in explanation of this action.

Moreover, the blackening of the bulb is less effective in absorbing the light in an inside coatedbulb, than in an exteriorly coated bulb. The outsidecoating backed up by the, glass of the bulb serves as a reflector to reflect back into'the bulb, a portion of the light emitted by the filament. A portion of the light is absorbed by theblackening on the bulb when the light first passes through the inside surface of the bulb and a further portion is absorbed when the light is reflected back into the bulb. This is known as double absorption and is eliminated in the inside coated bulb. v

As stated above, it is to be understood that this invention is not limited to the coating of incandescent lamp bulbs nor to the exact ingredients and proportions of the coating composition set forth therein nor to the exact method of applying the coating, but issusceptible to many modifications and adaptations. a

What is claimed is:

1. An incandescent, decorative electric lamp comprising an hermetically sealed bulb having on the interior surface of the light transmitting portion a visible superficial translucent coating of finely divided inorganic material.

2. An incandescent electric lamp com- I prising a bulb having on the interior surface of the light transmitting portion a visible superficial translucent coating of finely divided inorganic material substantially nonfading throughout the life of the lamp.

In testimony whereof, we have hereunto subscribed our names this 11th day of September,1924. i AARON MARTIN HAGEMAN. ALBERT FERDINAND LINDSTROM.

ableshort time after the coating is applied. 

